vCloud Director 8.20: How to change the owner of a vApp?

I'm not able to change the owner of a vApp using the SET_CIVAPP cmdlet. The  -Owner option in SET-CIVAPP is not working. I get the following error:

Set-CIVApp : 11/9/2017 8:42:39 PM    Set-CIVApp        Object reference not set to an instance of an object.

CategoryInfo          : NotSpecified: (:) [Set-CIVApp], CIException

FullyQualifiedErrorId : CloudImpl_UserService_GetUserForSysAdmin,VMware.VimAutomation.Cloud.Commands.Cmdlets.SetCIVApp